Coronary artery disease (CAD) places a major clinical (~16M) and financial (~$106B by 2030) burden on the U.S. healthcare system. The standard of care for many CAD patients with acute and stable coronary conditions involves percutaneous coronary intervention with stenting. Clinical outcomes following stenting are directly related to the achievement of adequate minimal stent/vascular area (i.e., full stent deployment) with full stent apposition against the vascular wall. Numerous studies have shown that up to 85% of all coronary stents are under-deployed and therefore require balloon post-dilatation to achieve proper stent expansion. Despite post-dilatation, up to 58% of stents still remain under-deployed. Although various factors affect stent deployment, only vascular/stent recoil and balloon under-expansion were shown to be the major factors causing stent under-expansion. Balloon under-expansion contributes to the majority of the stent under- deployment, which is not surprising given the in vivo reliance on inherently inaccurate manufacturer ex vivo pressure-diameter relationships. In our Phase I grant (R43 HL120517 - Coronary Post-Dilatation Catheter), a novel device was described which operates as a standard coronary post-dilatation catheter, but also provides real-time balloon dimension during inflation based on Ohm's law instead of empirical pressure-diameter relationships. The results of the Phase I study were extremely successful for both aims. The display console and CB catheter were updated in Aim #1 and validation of the CB catheter in injured swine coronary vessels showed extremely accurate post-dilatation in Aim #2 (i.e., in vivo CB balloon measurement accuracy bias = 0.05mm, which is highly acceptable clinically given this is at least an order of magnitude smaller (i.e., 10x smaller) than the 0.5mm standard stent divisions). In this Phase II application, we propose the next step of obtaining approval for an investigational device exemption (IDE) to conduct a human pilot study which will be used to assess primarily the device safety and secondarily device efficacy in a group of CAD patients. To accomplish these Phase II objectives, the following specific aims are proposed: 1) Final Animal Validation: To assess the safety and efficacy of the CB catheter system in a set of diseased animals in a good-laboratory practice (GLP) setting to be used for data submission to the FDA and institutional review boards (IRBs); and 2) Human Validation: To assess the safety and efficacy in a small group of humans (30 patients) in a two-center study. This Phase II study addresses a highly significant national and worldwide clinical need that can impact not just NHLBI, but many other mission areas of NIH. Successful completion of these proposed Aims will allow us to translate our research findings to a commercially available device that could drastically improve CAD patient outcomes.